Protocol – We use the off-resonant cascaded absorption (ORCA) [1]} protocol for our demonstration. ORCA comprises two counter-propagating optical fields that are two-photon resonant with an optical ladder transition of an atomic ensemble while being detuned from the intermediate transition by \(\Delta \)  (Fig. REF ), giving rise to absorption of the beams by exciting the atoms in the ensemble. The intense control pulse dresses the atomic system providing a broad virtual state to which the signal field couples efficiently, so that it may be completely absorbed. For large enough intermediate detuning, the absorption bandwidth is determined by the bandwidth of the control pulse. The input pulse excites a superposition of atoms in the ensemble of the \(|\textrm {g}\rangle - |\textrm {s}\rangle \)  transition. The state of the atomic ensemble after absorption of the signal is of the form \(\frac{1}{\sqrt{N}} \sum _{j=1}^N e^{i(\vec{k}_s - \vec{k}_c)\cdot \vec{v}_jt}\mathinner {|{g_1,\dots ,s_j,\dots ,g_N}\rangle }\)  where \(\mathinner {|{g(s)_j}\rangle }\)  labels the ground (storage) state of the \(j^\mathrm {th}\)  atom, \(N\)  is the total number of atoms, \(\vec{k}_{s(c)}\)  is the input (control) pulse wave vector, \(\vec{v}_j\)  is the velocity of the \(j^\mathrm {th}\)  atom. The collective dipole moment will emit light upon the application of a second control pulse after a storage time \(T\) , allowing the signal to be read out and completing the memory operation.
